1BPF(2)                     Linux Programmer's Manual                    BPF(2)
2
3
4

NAME

6       bpf - perform a command on an extended BPF map or program
7

SYNOPSIS

9       #include <linux/bpf.h>
10
11       int bpf(int cmd, union bpf_attr *attr, unsigned int size);
12

DESCRIPTION

14       The  bpf()  system  call  performs a range of operations related to ex‐
15       tended Berkeley Packet Filters.  Extended BPF (or eBPF) is  similar  to
16       the  original  ("classic")  BPF  (cBPF) used to filter network packets.
17       For both cBPF and eBPF programs, the  kernel  statically  analyzes  the
18       programs  before loading them, in order to ensure that they cannot harm
19       the running system.
20
21       eBPF extends cBPF in multiple ways, including the  ability  to  call  a
22       fixed set of in-kernel helper functions (via the BPF_CALL opcode exten‐
23       sion provided by eBPF) and access shared data structures such  as  eBPF
24       maps.
25
26   Extended BPF Design/Architecture
27       eBPF  maps  are  a generic data structure for storage of different data
28       types.  Data types are generally treated as binary  blobs,  so  a  user
29       just  specifies  the  size of the key and the size of the value at map-
30       creation time.  In other words, a key/value for a given map can have an
31       arbitrary structure.
32
33       A  user  process  can  create multiple maps (with key/value-pairs being
34       opaque bytes of data) and access them via file descriptors.   Different
35       eBPF  programs  can  access  the same maps in parallel.  It's up to the
36       user process and eBPF program to decide what they store inside maps.
37
38       There's one special map type, called a program array.  This type of map
39       stores  file  descriptors  referring  to  other  eBPF programs.  When a
40       lookup in the map is performed, the program flow is redirected in-place
41       to  the  beginning  of another eBPF program and does not return back to
42       the calling program.  The level of nesting has a fixed limit of 32,  so
43       that  infinite  loops cannot be crafted.  At run time, the program file
44       descriptors stored in the map can be modified, so program functionality
45       can  be  altered based on specific requirements.  All programs referred
46       to in a program-array map must have been  previously  loaded  into  the
47       kernel via bpf().  If a map lookup fails, the current program continues
48       its execution.  See BPF_MAP_TYPE_PROG_ARRAY below for further details.
49
50       Generally, eBPF programs are loaded by the user process  and  automati‐
51       cally  unloaded  when  the  process exits.  In some cases, for example,
52       tc-bpf(8), the program will continue to stay alive  inside  the  kernel
53       even  after  the  process that loaded the program exits.  In that case,
54       the tc subsystem holds a reference to the eBPF program after  the  file
55       descriptor  has been closed by the user-space program.  Thus, whether a
56       specific program continues to live inside the kernel depends on how  it
57       is further attached to a given kernel subsystem after it was loaded via
58       bpf().
59
60       Each eBPF program is a set of instructions that is safe  to  run  until
61       its  completion.   An in-kernel verifier statically determines that the
62       eBPF program terminates and is safe to execute.   During  verification,
63       the  kernel  increments  reference counts for each of the maps that the
64       eBPF program uses, so that the attached maps can't be removed until the
65       program is unloaded.
66
67       eBPF programs can be attached to different events.  These events can be
68       the arrival of network packets, tracing events,  classification  events
69       by network queueing  disciplines (for eBPF programs attached to a tc(8)
70       classifier), and other types that may be added in the  future.   A  new
71       event  triggers execution of the eBPF program, which may store informa‐
72       tion about the event in eBPF maps.  Beyond storing data, eBPF  programs
73       may call a fixed set of in-kernel helper functions.
74
75       The  same eBPF program can be attached to multiple events and different
76       eBPF programs can access the same map:
77
78           tracing     tracing    tracing    packet      packet     packet
79           event A     event B    event C    on eth0     on eth1    on eth2
80            |             |         |          |           |          ^
81            |             |         |          |           v          |
82            --> tracing <--     tracing      socket    tc ingress   tc egress
83                 prog_1          prog_2      prog_3    classifier    action
84                 |  |              |           |         prog_4      prog_5
85              |---  -----|  |------|          map_3        |           |
86            map_1       map_2                              --| map_4 |--
87
88   Arguments
89       The operation to be performed by the bpf() system call is determined by
90       the  cmd argument.  Each operation takes an accompanying argument, pro‐
91       vided via attr, which is a pointer to a union of type bpf_attr (see be‐
92       low).  The size argument is the size of the union pointed to by attr.
93
94       The value provided in cmd is one of the following:
95
96       BPF_MAP_CREATE
97              Create  a  map  and  return a file descriptor that refers to the
98              map.  The close-on-exec file descriptor flag (see  fcntl(2))  is
99              automatically enabled for the new file descriptor.
100
101       BPF_MAP_LOOKUP_ELEM
102              Look  up  an  element  by  key in a specified map and return its
103              value.
104
105       BPF_MAP_UPDATE_ELEM
106              Create or update an element (key/value pair) in a specified map.
107
108       BPF_MAP_DELETE_ELEM
109              Look up and delete an element by key in a specified map.
110
111       BPF_MAP_GET_NEXT_KEY
112              Look up an element by key in a specified map and return the  key
113              of the next element.
114
115       BPF_PROG_LOAD
116              Verify and load an eBPF program, returning a new file descriptor
117              associated with the program.  The close-on-exec file  descriptor
118              flag  (see  fcntl(2))  is automatically enabled for the new file
119              descriptor.
120
121              The bpf_attr union consists of various anonymous structures that
122              are used by different bpf() commands:
123
124           union bpf_attr {
125               struct {    /* Used by BPF_MAP_CREATE */
126                   __u32         map_type;
127                   __u32         key_size;    /* size of key in bytes */
128                   __u32         value_size;  /* size of value in bytes */
129                   __u32         max_entries; /* maximum number of entries
130                                                 in a map */
131               };
132
133               struct {    /* Used by BPF_MAP_*_ELEM and BPF_MAP_GET_NEXT_KEY
134                              commands */
135                   __u32         map_fd;
136                   __aligned_u64 key;
137                   union {
138                       __aligned_u64 value;
139                       __aligned_u64 next_key;
140                   };
141                   __u64         flags;
142               };
143
144               struct {    /* Used by BPF_PROG_LOAD */
145                   __u32         prog_type;
146                   __u32         insn_cnt;
147                   __aligned_u64 insns;      /* 'const struct bpf_insn *' */
148                   __aligned_u64 license;    /* 'const char *' */
149                   __u32         log_level;  /* verbosity level of verifier */
150                   __u32         log_size;   /* size of user buffer */
151                   __aligned_u64 log_buf;    /* user supplied 'char *'
152                                                buffer */
153                   __u32         kern_version;
154                                             /* checked when prog_type=kprobe
155                                                (since Linux 4.1) */
156               };
157           } __attribute__((aligned(8)));
158
159   eBPF maps
160       Maps  are  a  generic  data structure for storage of different types of
161       data.  They allow sharing of data between  eBPF  kernel  programs,  and
162       also between kernel and user-space applications.
163
164       Each map type has the following attributes:
165
166       *  type
167
168       *  maximum number of elements
169
170       *  key size in bytes
171
172       *  value size in bytes
173
174       The  following wrapper functions demonstrate how various bpf() commands
175       can be used to access the maps.  The functions use the cmd argument  to
176       invoke different operations.
177
178       BPF_MAP_CREATE
179              The  BPF_MAP_CREATE  command  creates a new map, returning a new
180              file descriptor that refers to the map.
181
182                  int
183                  bpf_create_map(enum bpf_map_type map_type,
184                                 unsigned int key_size,
185                                 unsigned int value_size,
186                                 unsigned int max_entries)
187                  {
188                      union bpf_attr attr = {
189                          .map_type    = map_type,
190                          .key_size    = key_size,
191                          .value_size  = value_size,
192                          .max_entries = max_entries
193                      };
194
195                      return bpf(BPF_MAP_CREATE, &attr, sizeof(attr));
196                  }
197
198              The new map has the type specified by map_type,  and  attributes
199              as  specified in key_size, value_size, and max_entries.  On suc‐
200              cess, this operation returns a file descriptor.  On error, -1 is
201              returned and errno is set to EINVAL, EPERM, or ENOMEM.
202
203              The key_size and value_size attributes will be used by the veri‐
204              fier during program loading to check that the program is calling
205              bpf_map_*_elem()  helper  functions with a correctly initialized
206              key and to check that the program doesn't access the map element
207              value  beyond the specified value_size.  For example, when a map
208              is created with a key_size of 8 and the eBPF program calls
209
210                  bpf_map_lookup_elem(map_fd, fp - 4)
211
212              the program will be rejected, since the in-kernel  helper  func‐
213              tion
214
215                  bpf_map_lookup_elem(map_fd, void *key)
216
217              expects to read 8 bytes from the location pointed to by key, but
218              the fp - 4 (where fp is the top of the stack)  starting  address
219              will cause out-of-bounds stack access.
220
221              Similarly,  when a map is created with a value_size of 1 and the
222              eBPF program contains
223
224                  value = bpf_map_lookup_elem(...);
225                  *(u32 *) value = 1;
226
227              the program will  be  rejected,  since  it  accesses  the  value
228              pointer beyond the specified 1 byte value_size limit.
229
230              Currently, the following values are supported for map_type:
231
232                  enum bpf_map_type {
233                      BPF_MAP_TYPE_UNSPEC,  /* Reserve 0 as invalid map type */
234                      BPF_MAP_TYPE_HASH,
235                      BPF_MAP_TYPE_ARRAY,
236                      BPF_MAP_TYPE_PROG_ARRAY,
237                      BPF_MAP_TYPE_PERF_EVENT_ARRAY,
238                      BPF_MAP_TYPE_PERCPU_HASH,
239                      BPF_MAP_TYPE_PERCPU_ARRAY,
240                      BPF_MAP_TYPE_STACK_TRACE,
241                      BPF_MAP_TYPE_CGROUP_ARRAY,
242                      BPF_MAP_TYPE_LRU_HASH,
243                      BPF_MAP_TYPE_LRU_PERCPU_HASH,
244                      BPF_MAP_TYPE_LPM_TRIE,
245                      BPF_MAP_TYPE_ARRAY_OF_MAPS,
246                      BPF_MAP_TYPE_HASH_OF_MAPS,
247                      BPF_MAP_TYPE_DEVMAP,
248                      BPF_MAP_TYPE_SOCKMAP,
249                      BPF_MAP_TYPE_CPUMAP,
250                      BPF_MAP_TYPE_XSKMAP,
251                      BPF_MAP_TYPE_SOCKHASH,
252                      BPF_MAP_TYPE_CGROUP_STORAGE,
253                      BPF_MAP_TYPE_REUSEPORT_SOCKARRAY,
254                      BPF_MAP_TYPE_PERCPU_CGROUP_STORAGE,
255                      BPF_MAP_TYPE_QUEUE,
256                      BPF_MAP_TYPE_STACK,
257                      /* See /usr/include/linux/bpf.h for the full list. */
258                  };
259
260              map_type selects one of the available map implementations in the
261              kernel.  For all map types, eBPF programs access maps  with  the
262              same   bpf_map_lookup_elem()  and  bpf_map_update_elem()  helper
263              functions.  Further details of the various map types  are  given
264              below.
265
266       BPF_MAP_LOOKUP_ELEM
267              The BPF_MAP_LOOKUP_ELEM command looks up an element with a given
268              key in the map referred to by the file descriptor fd.
269
270                  int
271                  bpf_lookup_elem(int fd, const void *key, void *value)
272                  {
273                      union bpf_attr attr = {
274                          .map_fd = fd,
275                          .key    = ptr_to_u64(key),
276                          .value  = ptr_to_u64(value),
277                      };
278
279                      return bpf(BPF_MAP_LOOKUP_ELEM, &attr, sizeof(attr));
280                  }
281
282              If an element is found, the operation returns  zero  and  stores
283              the  element's value into value, which must point to a buffer of
284              value_size bytes.
285
286              If no element is found, the operation returns -1 and sets  errno
287              to ENOENT.
288
289       BPF_MAP_UPDATE_ELEM
290              The  BPF_MAP_UPDATE_ELEM  command  creates or updates an element
291              with a given key/value in the map referred to by  the  file  de‐
292              scriptor fd.
293
294                  int
295                  bpf_update_elem(int fd, const void *key, const void *value,
296                                  uint64_t flags)
297                  {
298                      union bpf_attr attr = {
299                          .map_fd = fd,
300                          .key    = ptr_to_u64(key),
301                          .value  = ptr_to_u64(value),
302                          .flags  = flags,
303                      };
304
305                      return bpf(BPF_MAP_UPDATE_ELEM, &attr, sizeof(attr));
306                  }
307
308              The flags argument should be specified as one of the following:
309
310              BPF_ANY
311                     Create a new element or update an existing element.
312
313              BPF_NOEXIST
314                     Create a new element only if it did not exist.
315
316              BPF_EXIST
317                     Update an existing element.
318
319              On  success,  the  operation  returns zero.  On error, -1 is re‐
320              turned and errno is set to  EINVAL,  EPERM,  ENOMEM,  or  E2BIG.
321              E2BIG  indicates  that the number of elements in the map reached
322              the max_entries limit specified at map  creation  time.   EEXIST
323              will  be returned if flags specifies BPF_NOEXIST and the element
324              with key already exists in the map.  ENOENT will be returned  if
325              flags specifies BPF_EXIST and the element with key doesn't exist
326              in the map.
327
328       BPF_MAP_DELETE_ELEM
329              The BPF_MAP_DELETE_ELEM command deletes the element whose key is
330              key from the map referred to by the file descriptor fd.
331
332                  int
333                  bpf_delete_elem(int fd, const void *key)
334                  {
335                      union bpf_attr attr = {
336                          .map_fd = fd,
337                          .key    = ptr_to_u64(key),
338                      };
339
340                      return bpf(BPF_MAP_DELETE_ELEM, &attr, sizeof(attr));
341                  }
342
343              On  success,  zero is returned.  If the element is not found, -1
344              is returned and errno is set to ENOENT.
345
346       BPF_MAP_GET_NEXT_KEY
347              The BPF_MAP_GET_NEXT_KEY command looks up an element by  key  in
348              the  map  referred  to  by  the  file descriptor fd and sets the
349              next_key pointer to the key of the next element.
350
351                  int
352                  bpf_get_next_key(int fd, const void *key, void *next_key)
353                  {
354                      union bpf_attr attr = {
355                          .map_fd   = fd,
356                          .key      = ptr_to_u64(key),
357                          .next_key = ptr_to_u64(next_key),
358                      };
359
360                      return bpf(BPF_MAP_GET_NEXT_KEY, &attr, sizeof(attr));
361                  }
362
363              If key is  found,  the  operation  returns  zero  and  sets  the
364              next_key  pointer to the key of the next element.  If key is not
365              found, the operation returns zero and sets the next_key  pointer
366              to the key of the first element.  If key is the last element, -1
367              is returned and errno is set to ENOENT.   Other  possible  errno
368              values  are  ENOMEM, EFAULT, EPERM, and EINVAL.  This method can
369              be used to iterate over all elements in the map.
370
371       close(map_fd)
372              Delete the map referred to by the file descriptor map_fd.   When
373              the  user-space  program that created a map exits, all maps will
374              be deleted automatically (but see NOTES).
375
376   eBPF map types
377       The following map types are supported:
378
379       BPF_MAP_TYPE_HASH
380              Hash-table maps have the following characteristics:
381
382              *  Maps are created and destroyed by user-space programs.   Both
383                 user-space  and eBPF programs can perform lookup, update, and
384                 delete operations.
385
386              *  The kernel takes care of  allocating  and  freeing  key/value
387                 pairs.
388
389              *  The  map_update_elem() helper will fail to insert new element
390                 when the max_entries limit is reached.   (This  ensures  that
391                 eBPF programs cannot exhaust memory.)
392
393              *  map_update_elem() replaces existing elements atomically.
394
395              Hash-table maps are optimized for speed of lookup.
396
397       BPF_MAP_TYPE_ARRAY
398              Array maps have the following characteristics:
399
400              *  Optimized  for  fastest  possible  lookup.  In the future the
401                 verifier/JIT compiler may recognize lookup() operations  that
402                 employ  a constant key and optimize it into constant pointer.
403                 It is possible to optimize a  non-constant  key  into  direct
404                 pointer arithmetic as well, since pointers and value_size are
405                 constant for the life of the eBPF program.  In  other  words,
406                 array_map_lookup_elem()  may be 'inlined' by the verifier/JIT
407                 compiler while preserving concurrent access to this map  from
408                 user space.
409
410              *  All array elements pre-allocated and zero initialized at init
411                 time
412
413              *  The key is an array index, and must be exactly four bytes.
414
415              *  map_delete_elem() fails with the error EINVAL, since elements
416                 cannot be deleted.
417
418              *  map_update_elem()  replaces  elements in a nonatomic fashion;
419                 for atomic updates, a hash-table map should be used  instead.
420                 There  is however one special case that can also be used with
421                 arrays: the atomic  built-in  __sync_fetch_and_add()  can  be
422                 used  on  32 and 64 bit atomic counters.  For example, it can
423                 be applied on the whole value itself if it represents a  sin‐
424                 gle  counter,  or  in case of a structure containing multiple
425                 counters, it could be used on individual counters.   This  is
426                 quite often useful for aggregation and accounting of events.
427
428              Among the uses for array maps are the following:
429
430              *  As  "global"  eBPF variables: an array of 1 element whose key
431                 is (index) 0 and where the value is a collection of  'global'
432                 variables  which  eBPF programs can use to keep state between
433                 events.
434
435              *  Aggregation of tracing events into a fixed set of buckets.
436
437              *  Accounting of networking events, for example, number of pack‐
438                 ets and packet sizes.
439
440       BPF_MAP_TYPE_PROG_ARRAY (since Linux 4.2)
441              A  program  array  map  is a special kind of array map whose map
442              values contain only file descriptors  referring  to  other  eBPF
443              programs.   Thus,  both  the key_size and value_size must be ex‐
444              actly four bytes.  This map is  used  in  conjunction  with  the
445              bpf_tail_call() helper.
446
447              This  means  that  an  eBPF program with a program array map at‐
448              tached to it can call from kernel side into
449
450                  void bpf_tail_call(void *context, void *prog_map,
451                                     unsigned int index);
452
453              and therefore replace its own program flow with the one from the
454              program  at  the given program array slot, if present.  This can
455              be regarded as kind of a jump table to a different eBPF program.
456              The invoked program will then reuse the same stack.  When a jump
457              into the new program has been performed, it won't return to  the
458              old program anymore.
459
460              If  no  eBPF  program is found at the given index of the program
461              array (because the map slot doesn't contain a valid program file
462              descriptor,  the specified lookup index/key is out of bounds, or
463              the limit of 32 nested calls has been exceed), execution contin‐
464              ues  with the current eBPF program.  This can be used as a fall-
465              through for default cases.
466
467              A program array map is useful, for example, in tracing  or  net‐
468              working, to handle individual system calls or protocols in their
469              own subprograms and use their identifiers as an  individual  map
470              index.   This  approach  may result in performance benefits, and
471              also makes it possible to overcome the maximum instruction limit
472              of a single eBPF program.  In dynamic environments, a user-space
473              daemon might atomically replace individual subprograms  at  run-
474              time  with newer versions to alter overall program behavior, for
475              instance, if global policies change.
476
477   eBPF programs
478       The BPF_PROG_LOAD command is used to load an eBPF program into the ker‐
479       nel.   The return value for this command is a new file descriptor asso‐
480       ciated with this eBPF program.
481
482           char bpf_log_buf[LOG_BUF_SIZE];
483
484           int
485           bpf_prog_load(enum bpf_prog_type type,
486                         const struct bpf_insn *insns, int insn_cnt,
487                         const char *license)
488           {
489               union bpf_attr attr = {
490                   .prog_type = type,
491                   .insns     = ptr_to_u64(insns),
492                   .insn_cnt  = insn_cnt,
493                   .license   = ptr_to_u64(license),
494                   .log_buf   = ptr_to_u64(bpf_log_buf),
495                   .log_size  = LOG_BUF_SIZE,
496                   .log_level = 1,
497               };
498
499               return bpf(BPF_PROG_LOAD, &attr, sizeof(attr));
500           }
501
502       prog_type is one of the available program types:
503
504                  enum bpf_prog_type {
505                      BPF_PROG_TYPE_UNSPEC,        /* Reserve 0 as invalid
506                                                      program type */
507                      BPF_PROG_TYPE_SOCKET_FILTER,
508                      BPF_PROG_TYPE_KPROBE,
509                      BPF_PROG_TYPE_SCHED_CLS,
510                      BPF_PROG_TYPE_SCHED_ACT,
511                      BPF_PROG_TYPE_TRACEPOINT,
512                      BPF_PROG_TYPE_XDP,
513                      BPF_PROG_TYPE_PERF_EVENT,
514                      BPF_PROG_TYPE_CGROUP_SKB,
515                      BPF_PROG_TYPE_CGROUP_SOCK,
516                      BPF_PROG_TYPE_LWT_IN,
517                      BPF_PROG_TYPE_LWT_OUT,
518                      BPF_PROG_TYPE_LWT_XMIT,
519                      BPF_PROG_TYPE_SOCK_OPS,
520                      BPF_PROG_TYPE_SK_SKB,
521                      BPF_PROG_TYPE_CGROUP_DEVICE,
522                      BPF_PROG_TYPE_SK_MSG,
523                      BPF_PROG_TYPE_RAW_TRACEPOINT,
524                      BPF_PROG_TYPE_CGROUP_SOCK_ADDR,
525                      BPF_PROG_TYPE_LWT_SEG6LOCAL,
526                      BPF_PROG_TYPE_LIRC_MODE2,
527                      BPF_PROG_TYPE_SK_REUSEPORT,
528                      BPF_PROG_TYPE_FLOW_DISSECTOR,
529                      /* See /usr/include/linux/bpf.h for the full list. */
530                  };
531
532       For further details of eBPF program types, see below.
533
534       The remaining fields of bpf_attr are set as follows:
535
536       *  insns is an array of struct bpf_insn instructions.
537
538       *  insn_cnt is the number of instructions in the program referred to by
539          insns.
540
541       *  license  is  a  license string, which must be GPL compatible to call
542          helper functions marked gpl_only.  (The licensing rules are the same
543          as  for  kernel  modules,  so that also dual licenses, such as "Dual
544          BSD/GPL", may be used.)
545
546       *  log_buf is a pointer to a caller-allocated buffer in which  the  in-
547          kernel  verifier  can  store  the  verification  log.  This log is a
548          multi-line string that can be checked by the program author in order
549          to  understand how the verifier came to the conclusion that the eBPF
550          program is unsafe.  The format of the output can change at any  time
551          as the verifier evolves.
552
553       *  log_size  size  of the buffer pointed to by log_buf.  If the size of
554          the buffer is not large enough to store all verifier messages, -1 is
555          returned and errno is set to ENOSPC.
556
557       *  log_level  verbosity  level  of the verifier.  A value of zero means
558          that the verifier will not provide a log; in this case, log_buf must
559          be a NULL pointer, and log_size must be zero.
560
561       Applying close(2) to the file descriptor returned by BPF_PROG_LOAD will
562       unload the eBPF program (but see NOTES).
563
564       Maps are accessible from eBPF programs and are used  to  exchange  data
565       between  eBPF  programs  and  between eBPF programs and user-space pro‐
566       grams.  For example, eBPF programs can  process  various  events  (like
567       kprobe,  packets)  and store their data into a map, and user-space pro‐
568       grams can then fetch data from the map.   Conversely,  user-space  pro‐
569       grams  can  use  a map as a configuration mechanism, populating the map
570       with values checked by the eBPF program, which then modifies its behav‐
571       ior on the fly according to those values.
572
573   eBPF program types
574       The  eBPF  program  type  (prog_type)  determines  the subset of kernel
575       helper functions that the program may call.  The program type also  de‐
576       termines  the  program input (context)—the format of struct bpf_context
577       (which is the data blob passed into the eBPF program as the first argu‐
578       ment).
579
580       For  example,  a tracing program does not have the exact same subset of
581       helper functions as a socket filter program (though they may have  some
582       helpers  in common).  Similarly, the input (context) for a tracing pro‐
583       gram is a set of register values, while for a socket  filter  it  is  a
584       network packet.
585
586       The set of functions available to eBPF programs of a given type may in‐
587       crease in the future.
588
589       The following program types are supported:
590
591       BPF_PROG_TYPE_SOCKET_FILTER (since Linux 3.19)
592              Currently, the set of functions for  BPF_PROG_TYPE_SOCKET_FILTER
593              is:
594
595                  bpf_map_lookup_elem(map_fd, void *key)
596                                      /* look up key in a map_fd */
597                  bpf_map_update_elem(map_fd, void *key, void *value)
598                                      /* update key/value */
599                  bpf_map_delete_elem(map_fd, void *key)
600                                      /* delete key in a map_fd */
601
602              The bpf_context argument is a pointer to a struct __sk_buff.
603
604       BPF_PROG_TYPE_KPROBE (since Linux 4.1)
605              [To be documented]
606
607       BPF_PROG_TYPE_SCHED_CLS (since Linux 4.1)
608              [To be documented]
609
610       BPF_PROG_TYPE_SCHED_ACT (since Linux 4.1)
611              [To be documented]
612
613   Events
614       Once a program is loaded, it can be attached to an event.  Various ker‐
615       nel subsystems have different ways to do so.
616
617       Since Linux 3.19, the following call will attach the program prog_fd to
618       the socket sockfd, which was created by an earlier call to socket(2):
619
620           setsockopt(sockfd, SOL_SOCKET, SO_ATTACH_BPF,
621                      &prog_fd, sizeof(prog_fd));
622
623       Since Linux 4.1, the following call may be used to attach the eBPF pro‐
624       gram referred to by the file descriptor prog_fd to a  perf  event  file
625       descriptor,   event_fd,   that  was  created  by  a  previous  call  to
626       perf_event_open(2):
627
628           ioctl(event_fd, PERF_EVENT_IOC_SET_BPF, prog_fd);
629

RETURN VALUE

631       For a successful call, the return value depends on the operation:
632
633       BPF_MAP_CREATE
634              The new file descriptor associated with the eBPF map.
635
636       BPF_PROG_LOAD
637              The new file descriptor associated with the eBPF program.
638
639       All other commands
640              Zero.
641
642       On error, -1 is returned, and errno is set appropriately.
643

ERRORS

645       E2BIG  The eBPF program is too large or a map reached  the  max_entries
646              limit (maximum number of elements).
647
648       EACCES For  BPF_PROG_LOAD,  even  though  all  program instructions are
649              valid, the program has been rejected because it was  deemed  un‐
650              safe.   This  may  be  because it may have accessed a disallowed
651              memory region or an uninitialized stack/register or because  the
652              function  constraints  don't  match  the actual types or because
653              there was a misaligned memory access.  In this case, it is  rec‐
654              ommended  to  call  bpf()  again  with log_level = 1 and examine
655              log_buf for the specific reason provided by the verifier.
656
657       EBADF  fd is not an open file descriptor.
658
659       EFAULT One of the pointers (key or value or log_buf or insns)  is  out‐
660              side the accessible address space.
661
662       EINVAL The value specified in cmd is not recognized by this kernel.
663
664       EINVAL For BPF_MAP_CREATE, either map_type or attributes are invalid.
665
666       EINVAL For  BPF_MAP_*_ELEM  commands,  some  of  the  fields  of  union
667              bpf_attr that are not used by this command are not set to zero.
668
669       EINVAL For BPF_PROG_LOAD, indicates an attempt to load an invalid  pro‐
670              gram.   eBPF  programs can be deemed invalid due to unrecognized
671              instructions, the use of reserved fields, jumps  out  of  range,
672              infinite loops or calls of unknown functions.
673
674       ENOENT For  BPF_MAP_LOOKUP_ELEM  or BPF_MAP_DELETE_ELEM, indicates that
675              the element with the given key was not found.
676
677       ENOMEM Cannot allocate sufficient memory.
678
679       EPERM  The call was made  without  sufficient  privilege  (without  the
680              CAP_SYS_ADMIN capability).
681

VERSIONS

683       The bpf() system call first appeared in Linux 3.18.
684

CONFORMING TO

686       The bpf() system call is Linux-specific.
687

NOTES

689       Prior  to  Linux 4.4, all bpf() commands require the caller to have the
690       CAP_SYS_ADMIN capability.  From Linux 4.4 onwards, an unprivileged user
691       may create limited programs of type BPF_PROG_TYPE_SOCKET_FILTER and as‐
692       sociated maps.  However they may not store kernel pointers  within  the
693       maps and are presently limited to the following helper functions:
694
695       *  get_random
696       *  get_smp_processor_id
697       *  tail_call
698       *  ktime_get_ns
699
700       Unprivileged  access  may be blocked by writing the value 1 to the file
701       /proc/sys/kernel/unprivileged_bpf_disabled.
702
703       eBPF objects (maps and programs) can be shared between processes.   For
704       example,  after  fork(2), the child inherits file descriptors referring
705       to the same eBPF objects.  In addition, file descriptors  referring  to
706       eBPF  objects  can  be  transferred over UNIX domain sockets.  File de‐
707       scriptors referring to eBPF objects can be duplicated in the usual way,
708       using dup(2) and similar calls.  An eBPF object is deallocated only af‐
709       ter all file descriptors referring to the object have been closed.
710
711       eBPF programs can be written in a restricted C that is compiled  (using
712       the  clang  compiler) into eBPF bytecode.  Various features are omitted
713       from this restricted C, such as loops, global variables, variadic func‐
714       tions, floating-point numbers, and passing structures as function argu‐
715       ments.  Some examples can be found in the samples/bpf/*_kern.c files in
716       the kernel source tree.
717
718       The  kernel contains a just-in-time (JIT) compiler that translates eBPF
719       bytecode into native machine code for better performance.   In  kernels
720       before Linux 4.15, the JIT compiler is disabled by default, but its op‐
721       eration can be controlled by  writing  one  of  the  following  integer
722       strings to the file /proc/sys/net/core/bpf_jit_enable:
723
724       0  Disable JIT compilation (default).
725
726       1  Normal compilation.
727
728       2  Debugging  mode.   The  generated  opcodes are dumped in hexadecimal
729          into the kernel log.  These opcodes can then be  disassembled  using
730          the program tools/net/bpf_jit_disasm.c provided in the kernel source
731          tree.
732
733       Since Linux 4.15, the kernel may configured with the CONFIG_BPF_JIT_AL‐
734       WAYS_ON  option.  In this case, the JIT compiler is always enabled, and
735       the bpf_jit_enable is initialized to 1 and is immutable.  (This  kernel
736       configuration  option was provided as a mitigation for one of the Spec‐
737       tre attacks against the BPF interpreter.)
738
739       The JIT compiler for eBPF is currently available for the following  ar‐
740       chitectures:
741
742       *  x86-64 (since Linux 3.18; cBPF since Linux 3.0);
743       *  ARM32 (since Linux 3.18; cBPF since Linux 3.4);
744       *  SPARC 32 (since Linux 3.18; cBPF since Linux 3.5);
745       *  ARM-64 (since Linux 3.18);
746       *  s390 (since Linux 4.1; cBPF since Linux 3.7);
747       *  PowerPC 64 (since Linux 4.8; cBPF since Linux 3.1);
748       *  SPARC 64 (since Linux 4.12);
749       *  x86-32 (since Linux 4.18);
750       *  MIPS 64 (since Linux 4.18; cBPF since Linux 3.16);
751       *  riscv (since Linux 5.1).
752

EXAMPLES

754       /* bpf+sockets example:
755        * 1. create array map of 256 elements
756        * 2. load program that counts number of packets received
757        *    r0 = skb->data[ETH_HLEN + offsetof(struct iphdr, protocol)]
758        *    map[r0]++
759        * 3. attach prog_fd to raw socket via setsockopt()
760        * 4. print number of received TCP/UDP packets every second
761        */
762       int
763       main(int argc, char **argv)
764       {
765           int sock, map_fd, prog_fd, key;
766           long long value = 0, tcp_cnt, udp_cnt;
767
768           map_fd = bpf_create_map(BPF_MAP_TYPE_ARRAY, sizeof(key),
769                                   sizeof(value), 256);
770           if (map_fd < 0) {
771               printf("failed to create map '%s'\n", strerror(errno));
772               /* likely not run as root */
773               return 1;
774           }
775
776           struct bpf_insn prog[] = {
777               BPF_MOV64_REG(BPF_REG_6, BPF_REG_1),        /* r6 = r1 */
778               BPF_LD_ABS(BPF_B, ETH_HLEN + offsetof(struct iphdr, protocol)),
779                                       /* r0 = ip->proto */
780               BPF_STX_MEM(BPF_W, BPF_REG_10, BPF_REG_0, -4),
781                                       /* *(u32 *)(fp - 4) = r0 */
782               BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),       /* r2 = fp */
783               BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -4),      /* r2 = r2 - 4 */
784               BPF_LD_MAP_FD(BPF_REG_1, map_fd),           /* r1 = map_fd */
785               BPF_CALL_FUNC(BPF_FUNC_map_lookup_elem),
786                                       /* r0 = map_lookup(r1, r2) */
787               BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 2),
788                                       /* if (r0 == 0) goto pc+2 */
789               BPF_MOV64_IMM(BPF_REG_1, 1),                /* r1 = 1 */
790               BPF_XADD(BPF_DW, BPF_REG_0, BPF_REG_1, 0, 0),
791                                       /* lock *(u64 *) r0 += r1 */
792               BPF_MOV64_IMM(BPF_REG_0, 0),                /* r0 = 0 */
793               BPF_EXIT_INSN(),                            /* return r0 */
794           };
795
796           prog_fd = bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, prog,
797                                   sizeof(prog) / sizeof(prog[0]), "GPL");
798
799           sock = open_raw_sock("lo");
800
801           assert(setsockopt(sock, SOL_SOCKET, SO_ATTACH_BPF, &prog_fd,
802                             sizeof(prog_fd)) == 0);
803
804           for (;;) {
805               key = IPPROTO_TCP;
806               assert(bpf_lookup_elem(map_fd, &key, &tcp_cnt) == 0);
807               key = IPPROTO_UDP;
808               assert(bpf_lookup_elem(map_fd, &key, &udp_cnt) == 0);
809               printf("TCP %lld UDP %lld packets\n", tcp_cnt, udp_cnt);
810               sleep(1);
811           }
812
813           return 0;
814       }
815
816       Some complete working code can be found in the samples/bpf directory in
817       the kernel source tree.
818

SEE ALSO

820       seccomp(2), bpf-helpers(7), socket(7), tc(8), tc-bpf(8)
821
822       Both classic and extended BPF are explained in the kernel  source  file
823       Documentation/networking/filter.txt.
824

COLOPHON

826       This  page  is  part of release 5.10 of the Linux man-pages project.  A
827       description of the project, information about reporting bugs,  and  the
828       latest     version     of     this    page,    can    be    found    at
829       https://www.kernel.org/doc/man-pages/.
830
831
832
833Linux                             2020-11-01                            BPF(2)
Impressum